1. Field of the Invention
This invention relates generally to the field of automotive vehicle system diagnostics and more particularly to results evaluation leading to automatic diagnostic generation.
2. Description of the Related Art
Automotive vehicle system diagnostics procedures typically evaluate results of tests performed on a vehicle. Tests are either chosen by an engine analyzer system or are chosen manually based on a mechanic's knowledge of trouble symptoms. In the former case, the engine analyzer system instructs the operator to set up the test by attaching various test probes to the engine or system under test and performing certain actions such as maintaining a fixed RPM under load or cranking an engine during start.
The results of such tests, and knowledge about the vehicle or engine type, trouble symptoms, allowable limits, and other data can lead to a diagnosis of a problem. Diagnosis usually points to some corrective action such as parts replacement or system adjustment by the operator.
Marshall et al. in U.S. Pat. No. 4,373,186 teach a matrix method for obtaining diagnostics from engine test results. Tests are run on an engine, and results are entered as true/false dots in a matrix. Each dot or point in the matrix has an associated numeric value represented as a multi-digit binary number. The binary numbers represented by dots are combined by means of Boolean equations to yield a diagnostic which is reported to the operator. The results of tests can only be represented as true/false or pass/fail values (dots), and there is no way to ascertain whether or not a given test was performed.
There is a great need for a method that can integrate vehicle and engine attribute information with symptom data and test results to produce diagnostic results. Because test results are analog quantities, they should be represented by numbers rather than true/false or pass/fail values. It is very important to have the ability to perform intermediate arithmetic or logical analysis on test data, vehicle attributes, limits, and symptoms. The method should allow flexible equations and techniques to map intermediate results into final diagnostics. It is important that functions that perform this mapping be able to be evaluated recursively since it is not always possible to obtain complete diagnostic results in one pass. The generated diagnostic results should point to the causes of a problem, indicate corrective actions to be performed, and suggest additional tests to refine the diagnosis.